1. Field of the Invention
This invention relates to gas-liquid scrubbing apparatus. More particularly, it relates to an improved horizontal scrubbing apparatus having enhanced countercurrent gas-liquid contacting efficiency throughout the apparatus.
2. Description of the Prior Art
The growing awareness of the environmental hazards inherent in industrial and other commercial activities has resulted in ever more restrictive air pollution control regulations and concerns. Such concerns relate not only to air, water, and ground subjected to exposure to a variety of contaminants, but to the overall economic impact of measures available to satisfy environmental standards as reflected by pollution control laws and governmental regulations at all levels. In many instances, troublesome choices are confronted between the long range adverse environmental impact of industrial or other commercial operations and the adverse effect on the economic feasibility of the operations themselves resulting from efforts to provide effective and otherwise desirable pollution control measures. Accordingly, it is highly desirable and even vital that continued efforts be made to develop pollution control measures achieving a combination of more effective and efficient operation together with reduced cost for a particular operation.
For the treatment of industrial waste gases to be released to the atmosphere, the use of horizontal scrubbers has been known in the art as providing a desirable combination of efficiency and economy. Thus, Chemical Engineering, Nov. 21, 1966, p. 88 describes a horizontal scrubber which causes the gas stream to follow a tortuous path, resulting in higher contacting efficiency and increased gas treating capacity per unit size. Among other advantages cited are a reduction in structural support requirements, reduced duct work requirements and adaptability to limited overhead or floor space restrictions.
The Lloyd patent, U.S. Pat. No. 973,120, issued Oct. 18, 1910 illustrates that recent interest in the advantage of horizontal scrubbing devices is a reflection of very old technology updated in light of existing applications and environmental considerations. Lloyd discloses a horizontal scrubber in which gas flow is upward in each compartment containing scrubbing trays 8, with scrubbing liquid being discharged from spray nozzles 19 in each compartment for generally downward passage therein. Baffles 2 direct gas from each compartment downwardly for entrance into the next compartment at the bottom thereof. Liquid is collected in collection basins at the bottom of each compartment, with liquid overflowing from one basin to another countercurrent to the flow of gas through the unit. Liquid is pumped to the top of each compartment from the collection basin at the bottom thereof. As liquid is carried over with the gas exiting from each compartment, Lloyd achieves a further spraying action by positioning inclined plane 25 near the bottom of each baffle 2 causing the liquid to impinge thereon and form an additional spray through which the gas passes on its way to the next compartment. Scrubbing trays 8 are provided in each compartment. The Lloyd scrubber thus provides for a sinuous up and down course for the gas on its generally horizontal passage through the scrubber from one end to the other. The scrubbing liquid also passes eventually horizontally by overflow in the bottom of each compartment through the scrubber countercurrent to the direction of gas flow and passes downwardly in each compartment. With the scrubbing liquid continually being drawn from the bottom of each compartment and delivered to the top of the same compartment (p. 2, lines 13-21), however, full countercurrent flow of gas and liquid throughout the scrubber is not achieved. Similarly, the scrubber of the Chemical Engineering article referred to above does not achieve full countercurrent flow as the gas flow and liquid flow are both downward in the middle compartment of the device shown.
Rottmann et al, U.S. Pat. No. 1,677,409, discloses a plant for the absorption of gases and vapors, particularly of nitrous gases in the production of nitric acid, in which a series of concentric absorption towers packed with filling-rings or other acid-proof solid packing material is provided. The gaseous medium to be absorbed passes upwardly in the central tower and then successively upward through each of the annular towers around said central tower. Absorbing liquid is sprayed downwardly into each of said packed absorption towers, with separate discharge pipes being provided at the bottom of each packed tower. All of the packed concentric towers are arranged within superstructure c, so that leakage from any of the towers is contained within the plant. Countercurrent gas-liquid contact in each absorption tower is achieved with liquid from each tower passing separately to a point of utilization. The overall absorption plant with its necessary substructure may tend to obviate the advantage of reduced structural cost noted for present-day horizontal scrubbers as noted in the above-mentioned Chemical Engineering article. In addition, the earlier plant design, being relatively susceptible to plugging in operation and being difficult to clean because of the limited access available to internal parts of the plant, may tend to be impractical from a maintenance viewpoint in light of the current pollution control standards and the interrelated economic factors referred to above.
In a paper presented at the United States EPA "Flue Gas Desulfurization Symposium," Nov. 4, 1974, entitled "THE HORIZONTAL CROSS FLOW SCRUBBER", a horizontal scrubber is shown in which spray nozzles are positioned in a series of overhead rows for the downward spraying of scrubbing liquid on a flow of gas passing horizontally through the scrubber. While cross flow of gas and liquid is provided in this arrangement, full countercurrent flow is, of course, not achieved by such an arrangement.
There remains, on a continuing basis, a need for the development of pollution control systems in general, and gas scrubbing systems in particular, tailored to the specific needs of given applications. Such specific needs, of course, include ever increasing operation efficiency and reduced overall costs. By such development, the urgent requirements of environmental factors can be rendered more consistent with the equally compelling requirements of achieving pollution control within the framework of an economically feasible commercial operation.
It is an object of the present invention to provide an improved horizontal gas scrubbing apparatus.
It is another object of the invention to provide a horizontal scrubber having enhanced gas-liquid contacting efficiency.
It is a further object of the invention to provide a horizontal scrubber in which countercurrent gas-liquid contact is optimized.
It is a further object of the invention to provide a horizontal scrubber combining enhanced contacting efficiency with desirable compactness and structural economy.
With these and other objects in mind, the invention is hereinafter described with respect to various embodiments thereof, the novel features of which are set forth in the appended claims.